1. Field of the Invention
The present invention relates to a refrigeration cycle system with a refrigerant-to-refrigerant heat exchanger that allows heat exchange between a high-pressure refrigerant drawn from a liquid refrigerant receiver and directed to a variable throttle valve and a low-pressure refrigerant delivered from a refrigerant evaporator and directed to a refrigerant compressor. In particular, the present invention relates to a refrigeration cycle system which can control the amount of refrigerant in response to the level of subcooling of a refrigerant delivered from the refrigerant-to-refrigerant heat exchanger.
2. Description of the Related Art
As shown in FIG. 10A, a conventionally known refrigeration cycle system has an annular refrigerant circuit through which a gaseous refrigerant discharged from a discharge port of a compressor 101 is circulated through a sub-cooling condenser 102, a temperature controlled expansion valve 104, and an evaporator 105 back to a suction port of the compressor 101. As shown in FIG. 10B, also suggested is a refrigeration cycle system with an annular refrigerant circuit through which a gaseous refrigerant discharged from the discharge port of the compressor 101 is circulated through the sub-cooling condenser 102, a double-pipe refrigerant-to-refrigerant heat exchanger 103, the temperature controlled expansion valve 104, and the evaporator 105 back to the suction port of the compressor 101 (e.g., Japanese Patent Laid-Open Publication No. 2001-277842, PP. 1 to 7 and FIGS. 1 to 8).
The sub-cooling condenser 102 is a refrigerant condenser integrated with a liquid refrigerant receiver, in which a refrigerant condenser 121 for condensing a refrigerant into a liquid refrigerant, a liquid refrigerant receiver 122 for separating a refrigerant into liquid and gaseous refrigerants, a subcooler 123 for subcooling a liquid refrigerant and the like are integrated in one piece. On the other hand, employed as the temperature controlled expansion valve 104 is a so-called block-type (or box-type) expansion valve having an expansion valve body and a temperature-sensitive cylinder 106 incorporated into a cubic block in which are defined a high pressure refrigerant passageway serving as an inlet passageway to the evaporator 105 and a low pressure refrigerant passageway serving as an outlet passageway from the evaporator 105.
This refrigeration cycle system allows the double-pipe refrigerant-to-refrigerant heat exchanger 103 to exchange heat between a high pressure refrigerant flowing through a first refrigerant conduit 111 disposed at some midpoint in the high pressure refrigerant conduit (high pressure liquid line) and a low pressure refrigerant flowing through a second refrigerant conduit 112 disposed at some midpoint in the low pressure refrigerant conduit (low pressure suction conduit). This allows the low pressure refrigerant in the low pressure refrigerant conduit to absorb heat from the high pressure refrigerant in the high pressure refrigerant conduit, thereby making it possible to further subcool the high pressure liquid refrigerant delivered from the sub-cooling condenser 102. This in turn enables the liquid refrigerant to be supplied with stability to the valve hole of the temperature controlled expansion valve 104, thereby improving the performance of cooling the passenger compartment.
On the other hand, the high-pressure refrigerant in the high-pressure refrigerant conduit is to heat the low pressure refrigerant in the low pressure refrigerant conduit, thereby allowing the low pressure gaseous refrigerant delivered from the evaporator 105 and directed to the compressor 101 to be evaporated by superheating. This in turn prevents the refrigerant from being compressed in the compressor 101 and improves the performance of cooling the passenger compartment.
However, the prior art refrigeration cycle system employs a typical temperature controlled expansion valve 104 connected between the double-pipe refrigerant-to-refrigerant heat exchanger 103 and the evaporator 105, in which the level of superheating (SH) of the refrigerant on the outlet side of the evaporator 105 is sensed with the temperature-sensitive cylinder 106 incorporated in the low pressure refrigerant passageway to adjust the area of opening (the degree of valve opening) or the degree of throttle opening of the valve hole in the temperature controlled expansion valve 104.
With this arrangement, a high-temperature low-pressure gaseous refrigerant, which has been evaporated by superheating, flows normally (in a steady state) through the second refrigerant conduit 112 of the double-pipe refrigerant-to-refrigerant heat exchanger 103. Accordingly, a sufficiently large amount of heat is not exchanged between the high pressure refrigerant flowing through the first refrigerant conduit 11 of the double-pipe refrigerant-to-refrigerant heat exchanger 103 and the low pressure refrigerant flowing through the second refrigerant conduit 112. This causes the air passing through the evaporator 105 to be cooled with an insufficient degree of efficiency, thereby raising the problem of being unable to actually expect greater improvement in the performance of cooling the passenger compartment.